ABSTRACT Sleep impairments are ubiquitous in IDDs, and sleep problems profoundly impact quality of life and neurodevelopmental outcomes. The Center proposes a model research project, focused on the mechanisms underlying sleep impairments in IDDs using a multidisciplinary approach that includes a clinical component, animal models, and brain organoid models using patient-derived induced pluripotent stem cells. This project builds on findings from our previous IDDRC model project and the cells and circuits core, inspired by two striking findings: (1) in Dup15q syndrome, our investigators discovered profoundly abnormal sleep physiology, characterized by abnormal sleep spindles and attenuated slow-wave sleep (SWS), among patients who had undergone overnight clinical, with magnitude of these EEG abnormalities correlated with the degree of intellectual disability and (2) in Rett syndrome organoid models, our investigators quantified abnormal oscillatory activity in the earliest stages of development. For this project, we take a fully translational approach to study mechanisms underlying neural oscillations and sleep in Dup15q and Rett syndrome. In Aim 1 (Clinical), we verify abnormalities in sleep physiology (SWS and sleep spindle density) in clinical EEGs of young children with Dup15q syndrome and examine their relation to cognitive function. In Aim 2 (Preclinical model), we examine sleep physiology (SWS and spindles) and its effect on hippocampal and prefrontal ensemble activity in mouse models of Dup15q and Rett syndrome, performing EEG and simultaneous electrophysiological recordings and calcium imaging using a novel miniaturized microscope. In Aim 3 (Preclinical model), we investigate early neural network function in human cortical, subcortical, and hippocampal organoids from derived from Dup15q and Rett Syndrome iPSC using calcium imaging, electrophysiological recordings techniques, and transcriptomic analyses. This project leverages our center's strengths in both clinical and preclinical investigation of syndromic IDDs and capitalizes on active scientific collaborations between basic and clinical researchers in our center to understand sleep physiology, a fundamental and understudied problem in IDDs. By verifying the relationship between NREM sleep abnormalities and behavior in children with these syndromes and then, in model systems, determining the network and cellular basis of abnormal neural oscillations that are critical for memory formation and learning, this project will directly inform next steps for development of timely, effective treatments that may modulate sleep and, in turn, improve neurodevelopmental outcomes.